The term "old believer" generally refers to Russian Orthodox Christians who refused to accept the changes introduced into the liturgical services by the Patriarch Nikon in the mid-17th century. There are various synonyms for the term, including "staroobryadtsy" in Russian, "Old Ritualist," "Old Rite," or simply "Old Belief." These terms are often used interchangeably to refer to the conservative branch of the Russian Orthodox Church that has preserved its ancient liturgical practices for centuries. Today, old believers can be found not only in Russia but also in other countries where the Russian Orthodox Church has a presence, such as Romania, Bulgaria, Serbia, and Greece.